Specific immunoglobulins directed toward calmodulin were produced in rabbits. An enzyme-linked immunosorbent assay was developed for the measurement of calmodulin. In rat striatum calmodulin occurs in membrane-bound and soluble form. In striatal supernatant fractions it exists in free and protein (presumably, PDE)-bound form. Hence the regulation of calmodulin was viewed in terms of biochemical processes which modulate the distribution of this protein. Chronic treatment with haloperidol increases the membrane-bound calmodulin content. Studies on the turnover-rate of this protein failed to show a change in its synthesis-rate. From these results it can be inferred that chronic treatment with haloperidol may modify the binding affinity of calmodulin to its binding site at the membrane.